1. Field of the Invention
The present invention relates to a polyaniline derivative, particularly to a water-soluble self-acid-doped polyaniline blends.
2. Description of the Related Art
Polyaniline has a structure expressed by the following general formula:
wherein y=1−0 (Faraday Discuss Chem. Soc., 88 (1989) 317).
Polyaniline is a conjugate conductive polymer. The so-called conjugate conductive polymer has conjugate single bonds and double bonds alternately arranged on the backbone, whereby electrons can move along the molecular chain or across the molecular chains, wherefore a conjugate conductive polymer can conduct electricity. A conjugate conductive polymer has a very wide range of electric conductivity: from 10−12-10−9 S/cm in an undoped state to more than 103 S/cm in a doped state, which spans a range as huge as 1012-1015 times and covers the electric conductivities of insulating materials, semiconductors and conductors. The dopant concentration determines the conductivity of a conjugate conductive polymer. Most of conjugate conductive polymers are doped with external ions. The doping speed thereof is usually determined by the speed that the dopant ions diffuse in the polymer. However, a self-doped polyaniline does not need external dopant ions. When positive charges are introduced into the π-electron system of the backbone of the polymer, the positive charges can be offset by emigrating protons out of the polymer. Such a proton-hopping mechanism has ions with the smallest size and the highest mobility, which can provide a very high doping efficiency, prevent from ion loss and increase the stability of electric conduction.
Among conjugate conductive polymers, polyaniline has the following advantages: (1) it is made of a low-cost monomer and easy to synthesize; (2) it has superior stability in air and water; (3) its conductivity can be modified by doping a proton acid (not involving gain and loss of electrons) in addition to by a redox reaction (J. Chem. Soc., Faraday Trans., 82, 2385 (1986).; Macromolecules, 24, 1242 (1991).; Synth. Met., 13, 193 (1986)). Therefore, polyaniline has a very high potential. For examples, polyaniline may used as an electrode material because of the redox characteristic thereof; polyaniline may apply to a pH sensor because of the proton-exchange characteristic thereof; polyaniline can apply to a display because the electrochromic characteristic thereof. As polyaniline is very stable in air, it has been widely used in conductive plastics and the corrosion prevention engineering of ferrous and non-ferrous metals. Although polyaniline has many advantages, it also has disadvantages of low solubility and poor workability caused by the hardness and brittleness thereof. The disadvantages limit the application of polyaniline. The solubility of polyaniline can be improved via appropriately selecting the dopant agent thereof. Polyaniline can be blended with another polymeric material to improve the mechanical properties thereof. Nevertheless, polyaniline only dissolve in few organic solvents, such as NMP and DMSO. Therefore, the modification of polyaniline needs further researches.
Supercritical carbon dioxide has physical and chemical properties between those of the liquid phase and vapor phase of carbon dioxide. Therefore, supercritical carbon dioxide has the characteristics of gas and liquid simultaneously. Its viscosity resembles that of gas. However, its density, the spacing between its molecules, and its ability to dissolve materials are near those of liquid. Because of low viscosity, the transportation of supercritical carbon dioxide consumes less power than that of liquid. As supercritical carbon dioxide has a diffusion coefficient one hundred times that of liquid, it possesses superior mass transfer ability. As supercritical carbon dioxide almost has no surface tension, it has superior penetration ability and thus can easily penetrate a porous matter. Besides, carbon dioxide has characteristics of high chemical stability, non-toxicity, odorlessness, incombustibility, low cost, and high availability. Further, the critical pressure and critical temperature of carbon dioxide are not too high to economically reach. Therefore, supercritical carbon dioxide is very environment-friendly and economic-efficient. Supercritical carbon dioxide can apply to the fields of extraction, separation, cleaning, encapsulation, infusion, granulation and reaction.
Supercritical fluid has been applied to the reaction or modification of polymers. For example, Said-Galiyev, et al. performed a reaction of a diacid anhydride and a diamine in supercritical carbon dioxide at a temperature of 130-180° C. and under a pressure of 325 Bar to synthesize a polyimide; they also studied the relationship between the molecular weight of polyimide and the reaction conditions, wherein the molecular weight is determined with a viscosity method. The found that the following two factors influence the molecular weight of polyimide: (1) the molecular weight of polyimide obtained in a continuous-type reactor is greater than that obtained in a batch-type reactor; (2) the molecular weight increases with the reaction time (J. of Supercritical Fluids, 26, 147 (2003)). Tang, et al. soaked PPy (polypyrrole) and PS (polystyrene) in ScCO2 (supercritical CO2) at a temperature of 40° C. and under a pressure of 10.5 MPa for 1, 2, 3, 4, 9, 16, and 24 hours to synthesize PPy-PS composite films. The PPy-PS composite film obtained in the 24-hour soaking process has the best quality. When the PPy-PS composite film is doped by adding appropriate amount of FeCl3, the electric conductivity thereof can reach as high as 10−2 S/cm (European Polymer Journal, 39, 143 (2003)). Erkey, et al. used I2, which is soluble in supercritical carbon dioxide, as the oxidant. They soaked I2 and PU (polyurethane) in ScCO2 at a temperature of 50° C. and under a pressure of 13.7 MPa for 24 hours to implant the oxidant into PU. Next, they took out the PU and placed the PU in vacuum drying chambers. Next, they respectively filled PPy vapor into the vacuum drying chambers at temperatures of 0° C. and 21° C. and let PU react with PPy for 48 hours to form PPy-PU copolymers having fine workability and appropriate electric conductivities. The PPy-PU copolymers respectively have electric conductivities of 10−4 and 10−2 S/cm. When the PPy-PU copolymer is synthesized at the lower temperature, the content of PPy in the PPy-PU copolymer is increased by 20%, and the electric conductivity thereof is also increased (J. of Supercritical Fluids, 28, 233 (2004)). Satoshi, et al. mixed LA (lactic acid), DCC(N,N-dicyclohexy-carbodimide) and DMAP (4-dimethylamino pyridine) and synthesized PLLA (poly(L-lactic acid)) with the following three methods: (1) they heated LA to a temperature of 150° C. to become a melt-solid phase; then added DCC and DMAP into LA to synthesize PLLA; (2) they dissolved LA, DCC and DMAP in ScCO2 at a temperature of 80° C. and under a pressure of 3000 psig to synthesize PLLA; (3) they dissolved LA, DCC and DMAP in dicholomethane to synthesize PLLA. As the reactions of Method (2) and Method (3) took place in a homogenous phase, the PLLA of the two methods have higher molecular weights. As ScCO2 is non-toxic, harmless and recyclable, Method (2) is more environment-friendly and has higher economic-efficiency (Polymer, 45, 7839 (2004)).
Accordingly, the present invention synthesizes a water-soluble self-acid-doped polyaniline derivative in supercritical carbon dioxide, wherein the condensed aqueous solution of the polyaniline derivative can be directly cast into a film or coated on various substrates. The film has an electric conductivity of 10−4 S/cm, which meets the requirements of an ESD-prevention material (10−5 S/cm) and an antistatic material (10−6 S/cm).